Structured papermaking fabric

ABSTRACT

Disclosed are papermaking fabrics comprising a plurality of structuring elements disposed on a carrier structure. The fabrics are useful in the manufacture of tissue products having good caliper and smoothness without negatively affecting drying of the tissue product. The fabrics have structuring elements having a polygonal cross-sectional shape and a perimeter less than 3.6 mm, such as from about 1.4 to 3.6 mm. In certain instances the structuring elements may cover more than about 28 percent, such as from about 28 to about 35 percent, of the surface area of the web contacting surface of the carrier structure without adversely affecting drying. In this manner the amount of the nascent web that contacts the structuring elements and is molded into a smooth surface is maximized without exacerbating the negative affect to drying commonly associated with occluding a large portion of the surface area of the papermaking fabric.

BACKGROUND

In the manufacture of tissue products, particularly absorbent tissueproducts, there is a continuing need to improve the physical propertiesand final product appearance. It is generally known in the manufactureof tissue products that there is an opportunity to mold a partiallydewatered cellulosic web on a papermaking belt specifically designed toenhance the finished paper product's physical properties. Such moldingcan be applied by fabrics in an uncreped through-air dried process asdisclosed in U.S. Pat. No. 5,672,248 or in a wet pressed tissuemanufacturing process as disclosed U.S. Pat. No. 4,637,859. Wet moldingtypically imparts desirable physical properties independent of whetherthe tissue web is subsequently creped, or an uncreped tissue product isproduced.

However, absorbent tissue products are frequently embossed in asubsequent operation after their manufacture on the paper machine, whilethe dried tissue web has a low moisture content, to impart consumerpreferred visually appealing textures or decorative lines. Thus,absorbent tissue products having both desirable physical properties andpleasing visual appearances often require two manufacturing steps on twoseparate machines. Hence, there is a need for a single step papermanufacturing process that can provide the desired visual appearance andproduct properties. There is also a need to develop a papermanufacturing process that not only imparts visually discernable patternand product properties, but which does not affect machine efficiency andproductivity.

Previous attempts to combine the above needs, such as those disclosed inInternational Application Nos. PCT/US13/72220, PCT/US13/72231 andPCT/US13/72238, have utilized through-air drying fabrics having apattern extruded as a line element onto the fabric. The extruded lineelement may form either discrete or continuous patterns. While such amethod can produce textures, extrusion techniques are limited in thetypes of lines that may be formed resulting in reduced permeability ofthe through-air drying fabric. The reduced permeability in-turndecreases drying efficiency and negatively affects tissue machineefficiency and productivity.

As such, there remains a need for articles of manufacture and methods ofproducing tissue products having visually discernable patterns withimproved physical properties without losses to tissue machine efficiencyand productivity.

SUMMARY

The present inventors have now discovered a means of improving tissueweb drying by supporting the nascent web on a papermaking fabriccomprising a plurality of structuring elements disposed on a carrierstructure. More specifically the present inventors have discovered thatcertain desirable tissue product properties such as caliper andsmoothness may be optimized without negatively affecting drying of thetissue product by providing a papermaking fabric having structuringelements having a perimeter less than 3.6 mm, such as less than about3.0 mm, such as from about 1.4 to 3.6 mm, such as from about 1.6 toabout 2.4 mm, wherein the structuring elements cover more than about 28percent, such as from about 28 to about 35 percent, of the surface areaof the web contacting surface of the fabric. In this manner the amountof the nascent web that contacts the structuring elements and is moldedinto a smooth surface is maximized without exacerbating the negativeaffect to drying commonly associated with occluding a large portion ofthe surface area of the papermaking fabric.

Accordingly, it has now been discovered that relatively narrowstructuring elements, such as elements having a width of 0.7 mm or less,such as from 0.3 to 0.7 mm, have limited negative affect on drying,particularly the normalized drying rate, even when the elements cover arelatively large percentage of the papermaking surface area, such asmore than 28 percent and in some instances more than 30 percent. This iscounter to what was previously believed. Previously, it was believedthat an increase in the percentage of fabric covered by structuringelements resulted in a commensurate reduction in heat transfer, based onthe theoretical drying rate:

DR=q/φ=hA(T _(supply) −T _(sheet))

Where q is the heat transfer in W/m², φ is the latent heat of the waterdried in j/g, DR is the drying rate in g/s m², h is the heat transfercoefficient in W/m² C, A is the area open to the flow in m²/m², and T istemperature. In view of the foregoing, it was believed that when thecoverage area (A) is reduced the drying rate should be reduced by thesame amount. It has now been discovered, however, that the dominantfactor affecting drying rate is the relative size of the structuringmember, and that the coverage area may be increased so long as the sizeof the structuring element is optimized.

Thus, in certain embodiments the present invention provides apapermaking belt comprising a woven carrier structure having a machinecontacting surface and an opposite web contacting surface and aplurality of structuring elements, which may be formed from a liquid andair impervious material such as silicone or polyurethane, disposed onthe web contacting surface. The structuring elements are preferablyshaped and sized to enable molding of the nascent web and to minimizenegative impacts to drying and as such generally have a cross-sectionalperimeter less than 3.6 mm, such as less than about 3.0 mm, such as lessthan about 2.4 mm, such as less than about 2.0 mm, such as from about1.4 to 3.6 mm, such as from about 1.6 to about 3.0 mm.

When viewed in the cross-section perpendicular to the X-Y plane of thepapermaking belt the structuring elements may have any number ofdifferent cross-sectional shapes such as, for example, polygonal,semicircular or elliptical. In certain preferred embodiments thestructuring member has a polygonal cross-sectional shape such as, forexample, a trapezoid, a parallelogram, a rectangle, a rhombus, or asquare. Regardless of the cross-sectional shape, the structuringelements generally have a cross-sectional perimeter less than 3.6 mm,such as less than about 3.0 mm, such as less than about 2.4 mm, such asless than about 2.0 mm, such as from about 1.4 to 3.6 mm, such as fromabout 1.6 to about 3.0 mm.

Structuring elements can provide a means for deflecting papermakingfibers in the Z-direction as the nascent web is molded and dried whilesupported by the fabric. The amount of fiber deflection and the physicalproperties of the resulting tissue web such as caliper, density andsurface topography may be affected to some extent by the size and shapeof the structuring elements. Thus, in certain embodiments, it may bepreferred that the structuring member have a Z-directional heightgreater than about 0.4 mm, such as greater than about 0.5 mm, and morepreferably greater than about 0.6 mm, such as from about 0.4 to about1.2 mm and more preferably from about 0.4 to about 0.8 mm. In otherembodiments the structuring member have width, generally measured in thecross-machine direction (CD) across the widest portion of the elementand parallel to the upper surface plane of the carrier structure, of 0.7mm or less, such as less than about 0.6 mm, such as less than about 0.5mm, such as from about 0.4 to 0.7 mm.

In other instances fiber deflection and the physical properties of theresulting tissue web such as caliper, density and surface topography, aswell as the effective drying of the web may be affected by the aspectratio of the structuring member, or the ratio of the width toZ-directional height. For optimal drying and physical properties theaspect ratio, which is generally the ratio of the element height to theelement width, may be from about 2:1 to 2:3, such as from 1.5:1 to about1:1.

In addition to the size and the shape of the structuring member thephysical properties of the resulting tissue web, as well as the dryingof the web, may be influenced by the relative percentage of the carrierstructure that is covered by the structuring elements. For example, itmay be desirable to provide the finished tissue web with a plurality ofrelatively smooth, elevated portions that are brought in contact with auser's skin in-use, yet at the same time minimize the amount of the webthat is contacted by the structuring elements, which are generallyimpermeable to air and water, so as not to impede drying. By providing astructuring member having a cross-sectional perimeter less than 3.6 mm,such as from about 1.4 to 3.6 mm, such as from about 1.6 to about 2.4mm, it has been discovered that the relative area of the carrierstructure that may be covered by structuring elements may be relativelyhigh such as greater than about 28 percent, such as greater than about30 percent and more preferably greater than about 32 percent, such asfrom about 28 to about 35 percent and more preferably from about 30 toabout 32 percent, without negatively affecting drying of the nascentweb. As such a finished tissue web having a relatively high degree ofrelatively smooth, elevated portions may be produced without negativelyaffecting drying of the nascent web.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a papermaking fabric useful in themanufacture of tissue webs according to one embodiment of the presentinvention;

FIG. 2 is top view of a papermaking fabric useful in the manufacture oftissue webs according to one embodiment of the present invention;

FIG. 3 is a cross section view of a papermaking fabric taken throughline 3-3 of FIG. 2;

FIG. 4 is a cross-sectional image of a papermaking fabric taken using aKeyence VHX-5000 Digital Microscope (Keyence Corporation, Osaka, Japan)at a magnification of 20×;

FIG. 5 is a top view of a papermaking fabric taken using a KeyenceVHX-5000 Digital Microscope (Keyence Corporation, Osaka, Japan) at amagnification of 20×;

FIG. 6 is an image of the papermaking fabric of FIG. 5 that has beenprocessed to calculate the element coverage area as described in theTest Method section;

FIG. 7 is a plot of the heat transfer coefficient (drying ratenormalized by the through-air dryer supply temperature) versus elementcoverage area (x-axis) at a through-air dryer supply temperature of 300°F. for through-air drying fabrics having structuring elements havingwidths of 0.9 mm (●), 0.8 mm (x), 0.7 mm (▴), and 0.6 mm (▪);

FIG. 8 is a plot of the heat transfer coefficient (drying ratenormalized by the through-air dryer supply temperature) versus elementperimeter (x-axis) at a through-air dryer supply temperature of 300° F.for through-air drying fabrics having structuring elements having widthsof 0.9 mm (●), 0.8 mm (x), 0.7 mm (▴), and 0.6 mm (▪); and

FIG. 9 is a plot of the drying loss factor (y-axis) versus elementcoverage area (x-axis) at a through-air dryer supply temperature of 300°F. for through-air drying fabrics having structuring elements havingwidths of 0.9 mm (●), 0.8 mm (x), 0.7 mm (▴), and 0.6 mm (▪).

DEFINITIONS

As used herein, the term “papermaking fabric” means any woven fabricused for making a cellulosic web such as a tissue sheet, either by awet-laid process or an air-laid process. Specific papermaking fabricswithin the scope of this invention include forming fabrics; transferfabrics conveying a wet web from one papermaking step to another, suchas described in U.S. Pat. No. 5,672,248; molding, shaping, or impressionfabrics where the web is conformed to the structure through pressureassistance and conveyed to another process step, as described in U.S.Pat. No. 6,287,426; creping fabrics as described in U.S. Pat. No.8,394,236; embossing fabrics as described in U.S. Pat. No. 4,849,054;structured fabric adjacent a wet web in a nip as described in U.S. Pat.No. 7,476,293; or through-air drying fabric as described in U.S. Pat.Nos. 5,429,686, 6,808,599 B2 and 6,039,838. The fabrics of the inventionare also suitable for use as molding or air-laid forming fabrics used inthe manufacture of non-woven, non-cellulosic webs, such as baby wipes.

As used herein the term “machine direction,” designated MD, is thedirection parallel to the flow of the fibrous web through the web-makingequipment.

As used herein the term “cross machine direction,” designated CD, is thedirection perpendicular to the machine direction in the X-Y plane.

As used herein the term “width” when referring to a structuring membergenerally refers to the widest portion of a cross-sectional portion ofthe element in the cross-machine direction (CD). Generally width ismeasured at the widest point of the element and parallel to the uppersurface plane of the carrier structure.

As used therein the term “height” when referring to a structuring memberis the Z-direction height of a member extending from the carrierstructure and is generally measured between the upper surface plane ofthe carrier structure and the upper surface plane of the element.

As used herein the term “aspect ratio” when referring to a structuringmember is the ratio of the element height to the element width.

As used herein the terms “effective perimeter” and “perimeter” whenreferring to a structuring member is the total perimeter of across-sectional portion of the element. Generally the perimeter of across-sectional portion of the element is a continuous line forming theboundary of a closed geometric figure.

As used herein the term “coverage area” generally refers to percentageof the carrier structure's upper surface area that is covered bystructural elements as measured using a Keyence VHX-5000 DigitalMicroscope (Keyence Corporation, Osaka, Japan) and described in the TestMethods section below.

As used herein the term “line element” refers to structuring elements inthe shape of a line, which may be a continuous, discrete, interrupted,and/or partial line with respect to the carrier structure on which it ispresent. The line element may be of any suitable shape such as straight,bent, kinked, curled, curvilinear, serpentine, sinusoidal, and mixturesthereof that may form regular or irregular periodic or non-periodiclattice work of structures wherein the line element exhibits a lengthalong its path of at least 10 mm. In one example, the line element maycomprise a plurality of discrete elements, such as dots and/or dashesfor example, that are oriented together to form a line element.

As used herein the term “continuous” when referring to a structuringmember generally refers to an element disposed on a carrier structureuseful in forming a tissue web that extends without interruptionthroughout one dimension of the carrier structure.

As used herein the term “discrete element” when referring to astructuring member generally refers to separate, unconnected elementsdisposed on a carrier structure useful in forming a tissue web that donot extend continuously in any dimension of the support structure or thetissue web as the case maybe.

As used herein the term “curvilinear element” when referring to astructuring member generally refers to any structuring member thatcontains either straight sections, curved sections, or both that aresubstantially connected visually. Curvilinear structuring elements mayappear as undulating lines, substantially connected visually, formingsignatures or patterns.

As used herein “decorative pattern” refers to any non-random repeatingdesign, figure, or motif. It is not necessary that the curvilinearstructuring elements form recognizable shapes, and a repeating design ofthe curvilinear structuring elements is considered to constitute adecorative pattern.

DETAILED DESCRIPTION

With reference now to FIGS. 1-3 a papermaking fabric 10 according to thepresent invention is illustrated. The papermaking fabric 10 comprises acarrier structure 30 having a web contacting surface 64 and a machinecontacting surface 62. In use, web contacting surface 64 is generallythe side of the fabric 10 on which fibers, such as papermaking fibers,are deposited. The web contacting surface forms an X-Y plane, where Xand Y can correspond generally to the cross-machine direction (CD) andmachine direction (MD), respectively, when using the belt in themanufacturing of tissue webs. One skilled in the art will appreciatethat the symbols “X,” “Y,” and “Z” designate a system of Cartesiancoordinates, wherein mutually perpendicular “X” and “Y” define areference plane formed by the web contacting surface 64 of thepapermaking fabric 10 when disposed on a flat surface, and “Z” defines adirection orthogonal to the X-Y plane. The person skilled in the artwill appreciate that the use of the term “plane” does not requireabsolute flatness or smoothness of any portion or feature described asplanar. In fact, a portion of the web contacting surface of the fabricmay consist of a woven fabric having a textured upper surface, which maybe useful in imparting patterns or physical properties to a tissue web,yet be defined as being generally planar or as having a surface plane.

As used herein, the term “Z-direction” designates any directionperpendicular to the X-Y plane. Analogously, the term “Z-dimension”means a dimension, distance, or parameter measured parallel to theZ-direction and can be used to refer to dimensions such as the height ofdiscrete primary elements or the thickness (or height or caliper), ofthe secondary elements. It should be carefully noted, however, that anelement that “extends” in the Z-direction does not need itself to beoriented strictly parallel to the Z-direction; the term “extends in theZ-direction” in this context merely indicates that the element extendsin a direction which is not parallel to the X-Y plane. Analogously, anelement that “extends in a direction parallel to the X-Y plane” does notneed, as a whole, to be parallel to the X-Y plane; such an element canbe oriented in the direction that is not parallel to the Z-direction.

One skilled in the art will also appreciate that any given structuringmember may not necessarily have an upper surface that is substantiallyflat throughout its entire length, yet the upper most portion of themember may generally define a plane. Irregularities in the upper surfaceof structuring elements may result from the elements being manufacturedby depositing a polymeric material, which may be flowable to a certainextent, onto a woven carrier structure having an upper surface of whichis not entirely flat, but has a degree of texture. Nonetheless, asillustrated in FIG. 1 and discussed herein, the structuring member 40being disposed on a carrier structure 30 having a substantially flatupper surface 48 and the macroscopic “X-Y” plane is conventionally usedherein for the purpose of describing relative geometry of severalelements of the structuring member 40.

As shown in FIG. 1, the structuring elements 40 are provided in the formof substantially similarly shaped continuous line elements. Eachstructuring element 40 extends in the Z-direction on the web contactingside 64 of the carrier structure 30. The structuring elements 40 have agenerally square cross-sectional shape with spaced apart relativelystraight, parallel sidewalls 45, 47. While the illustrated structuringelements have a generally square cross-sectional shape, the invention isnot so limited and the elements may have a variety of shapes such as,for example, polygonal, semicircular or elliptical. In certain preferredembodiments the line elements have a polygonal cross-sectional shapesuch as, for example, a trapezoid, a parallelogram, a rectangle, arhombus, or a square. Further, the structuring element sidewalls 45, 47and top surfaces 48 can be relatively straight and planar, such asillustrated in FIG. 1, or they may be curved, partially straight andpartially curved, or irregular when viewed in cross-section. It shouldbe noted that the drawings schematically show the sidewalls 45, 47 andtop surface 48 as straight lines for ease of illustration only.

Although each of the structuring elements 40 have similar shapes anddimensions, the invention is not so limited, and a variety of differentshapes and sizes may be employed. For example, each of the line elementscan be individually sized, shaped, and spaced. The illustratedstructuring elements 40 are continuous line elements, each having agenerally flat distal portion 48 (portion distal from the carrierstructure 30) providing the papermaking fabric 10 with a relativelyuniform second upper surface plane 74 (as illustrated in FIG. 3). Inthis manner each of the structuring elements 40 have a Z-directionheight (h), measured from the upper surface plane 72 of the webcontacting surface 64 of the carrier structure 30. Although notillustrated in FIGS. 1-3, the structuring elements may also vary inrelation to one another in terms of height or width. Further, the heightand width of a given line element need not be uniform along its entirelength, but can vary depending on the method of manufacturing theelement or according to the desired physical properties of the finishedtissue web.

There are virtually an infinite number of shapes, sizes, spacing andorientations that may be chosen for the structuring elements. The actualshapes, sizes, orientations, and spacing can be specified andmanufactured by additive manufacturing processes based on the desiredproperties of the finished tissue web such as caliper, sheet bulk,surface smoothness and aesthetic appearance. The improvement of thepresent invention is that the shapes, sizes, spacing, and orientationsof the structuring element are such that they provide the finishedtissue web with desirable physical properties, such as caliper, sheetbulk and surface smoothness, without negatively affecting drying of thetissue web. As such the structuring elements are generally designed suchthat a sufficient amount of the nascent web is contacted by and moldedinto the elements, but the amount of the web that is effectivelyrendered impermeable because of its contact with the elements isminimized.

For optimal molding of the web and minimal negative impact to drying,the shape of the elements may be modified such that the cross-sectionalperimeter is less than 3.6 mm, such as less than about 3.0 mm, such asless than about 2.4 mm, such as less than about 2.0 mm, such as fromabout 1.4 to 3.6 mm, such as from about 1.6 to about 3.0 mm. In otherembodiments the aspect ratio may be modified to promote drying andimpart the resulting web with the desired physical properties andaesthetic appearance. For example, optimal drying and physicalproperties of the tissue product may be obtained by using a through-airdrying fabric having structuring elements with an aspect ratio, which isgenerally the ratio of the element height to the element width, fromabout 2:1 to 2:3, such as from 1.5:1 to about 1:1.

With continued reference to FIGS. 1-3, the carrier structure 30comprises a pair of opposed major surfaces—a web contacting surface 64from which the structuring elements 40 extend and a machine contactingsurface 62. Machinery employed in a typical papermaking operation iswell known in the art and may include, for example, vacuum pickup shoes,rollers, and drying cylinders. In one embodiment the belt comprises athrough-air drying fabric useful for transporting an embryonic tissueweb across drying cylinders during the tissue manufacturing process. Insuch embodiments the web contacting surface 64 supports the embryonictissue web, while the opposite surface, the machine contacting surface62, contacts the through-air dryer.

Generally the structuring element 40 is disposed on the web-contactingsurface 64 for cooperating with, and structuring of, the wet fibrous webduring manufacturing. In a particularly preferred embodiment the webcontacting surface 64 comprises a plurality of spaced apartthree-dimensional elements 40 distributed across the web-contactingsurface 64 of the carrier structure 30 such that the relative area ofthe carrier structure covered by the elements may be relatively highsuch as greater than about 28 percent, such as greater than about 30percent and more preferably greater than about 32 percent, such as fromabout 28 to about 35 percent and more preferably from about 30 to about32 percent, without negatively affecting drying of the nascent web. Assuch a finished tissue web having a relatively high degree of relativelysmooth, elevated portions may be produced without negatively affectingdrying of the nascent web.

In addition to structuring elements 40 the web-contacting surface 64preferably comprises a plurality of continuous landing areas 60. Thelanding areas 60 are generally bounded by the elements 40 andcoextensive with the upper surface plane 72 of the web contactingsurface 64. Landing areas 60 are generally permeable to liquids andallow water to be removed from the cellulosic tissue web by theapplication of differential fluid pressure, by evaporative mechanisms,or both when drying air passes through the embryonic tissue web while onthe papermaking belt 10 or a vacuum is applied through the belt 10.Without being bound by any particularly theory, it is believed that thearrangement of elements and landing areas allow the molding of theembryonic web causing fibers to deflect in the z-direction and generatethe caliper of, and patterns on the resulting tissue web.

The carrier structure 30 has two principle dimensions—a machinedirection (“MD”), which is the direction within the plane of the belt 10parallel to the principal direction of travel of the tissue web duringmanufacture and a cross-machine direction (“CD”), which is generallyorthogonal to the machine direction. The carrier structure 30 isgenerally permeable to liquids and air. In one particularly preferredembodiment the carrier structure is a woven fabric. The carrierstructure may be substantially planar or may have a three dimensionalsurface defined by ridges. In one embodiment the carrier structure is asubstantially planar woven fabric such as a multi-layered plain-wovenfabric 30 having base warp yarns 32 interwoven with shute yarns 34 in a1×1 plain weave pattern. One example of a suitable substantially planarwoven fabric is disclosed in U.S. Pat. No. 8,141,595, the contents ofwhich are incorporated herein in a manner consistent with the presentinvention. In a particularly preferred embodiment, the carrier structurecomprises a substantially planar woven fabric wherein the plain-weaveload-bearing layer is constructed so that the highest points of both theload-bearing shutes 34 and the load-bearing warps 32 are coplanar andcoincident with the upper surface plane 72 of the web contacting surface64.

A plurality of structuring elements 40 that may, such as in theembodiments illustrated in FIGS. 1-3, comprise a plurality of continuousline elements having a substantially rectangular cross-section, aredisposed on the web-contacting surface 64 of the carrier structure 30.Each structuring element 40 has a first dimension in a first direction(x) in the plane of the top surface area, a second dimension in a seconddirection (y) in the plane of the top surface area, the first and seconddirections (x, y) being at right angles to each other. The extent of theelement 40 in the first direction (x) generally defines the elementwidth (w). The continuous element 40 further comprises a top surface 48extending substantially along the second direction (y) and a pair ofopposed sidewalls 45, 47 extending in the z-direction and having a meanheight (h). These dimensions being defined when the belt is in anuncompressed state.

The structuring elements 40 generally extend in the z-direction(generally orthogonal to both the machine direction and cross-machinedirection) above the upper surface plane 72 of the web contactingsurface 64. As noted previously, in certain embodiments, the elements 40may have straight, parallel sidewalls 45, 47 providing the structuringelements 40 with a width (w), and a height (h) and the elements 40 maybe similarly sized.

In certain embodiments the elements may have a Z-directional heightgreater than about 0.4 mm, such as greater than about 0.5 mm, and morepreferably greater than about 0.6 mm, such as from about 0.4 to about1.2 mm and more preferably from about 0.4 to about 0.8 mm. In aparticularly preferred embodiment the height of the elements issubstantially similar and ranges from about 0.4 to about 1.2 mm and morepreferably from about 0.4 to about 0.8 mm.

Further, the structuring elements 40 may have a width (w), generallymeasured in the cross-machine direction (CD) across the widest portionof the element and parallel to the upper surface plane of the carrierstructure, of 0.7 mm or less, such as less than about 0.6 mm, such asless than about 0.5 mm, such as from about 0.4 to 0.7 mm.

While the height (h) and width (w) of the elements may be varied, it isgenerally preferred that the elements have a cross-sectional perimeterless than 3.6 mm, such as less than about 3.0 mm, such as less thanabout 2.4 mm, such as less than about 2.0 mm, such as from about 1.4 to3.6 mm, such as from about 1.6 to about 3.0 mm. In other instances theelements have a height (h) and width (w) such that the aspect ratio isfrom about 2:1 to 2:3, such as from 1.5:1 to about 1:1.

In a particularly preferred embodiment the structuring elements 40 haveplanar sidewalls 45, 47 such that the cross-section of the element hasan overall square or rectangular shape. However, it is to be understoodthat the design element may have other cross-sectional shapes, such as atrapezoid or a parallelogram, which may also be useful in producing highbulk tissue products according to the present invention. Accordingly, ina particularly preferred embodiment the structuring elements 40preferably have planar sidewalls 45, 47 and a square cross-section wherethe width (w) and height (h) are equal and are 0.7 mm or less, such asless than about 0.6 mm, such as less than about 0.5 mm, such as fromabout 0.4 to 0.7 mm.

The spacing and arrangement of the structuring elements relative to oneanother may vary depending on the desired tissue product properties andappearance. In one embodiment a plurality of elements extendcontinuously throughout one dimension of the belt and each element inthe plurality is spaced apart from the adjacent element. Thus, theelements may be spaced apart across the entire cross-machine directionof the belt, may endlessly encircle the belt in the machine direction,or may run diagonally relative to the machine and cross-machinedirections. Of course, the directions of the elements alignments(machine direction, cross-machine direction, or diagonal) discussedabove refer to the principal alignment of the elements. Within eachalignment, the elements may have segments aligned at other directions,but aggregate to yield the particular alignment of the entire elements.

Generally the elements are spaced apart from one another so as to definea landing area there-between. In use, as the embryonic tissue web isformed fibers are deflected in the z-direction by the continuouselements, however, the spacing of elements is such that the webmaintains a relatively uniform density. This arrangement provides thebenefits of improved web extensibility, increased sheet bulk, bettersoftness, and a more pleasing texture.

If the individual elements are too high, or the landing area is toosmall, the resulting sheet may have excessive pinholes and insufficientcompression resistance and cross-machine direction physical properties,such as stretch, and be of poor quality. Further, tensile strength maybe degraded if the span between elements greatly exceeds the fiberlength. Conversely, if the spacing between adjacent elements is toosmall the tissue will not mold into the landing areas without rupturingthe sheet, causing excessive sheet holes, poor strength, and poor paperquality.

In addition to varying the spacing and arrangement of the elements alongthe carrier structure, the shape of the element may also be varied. Forexample, in one embodiment, the elements are substantially sinusoidaland are arranged substantially parallel to one another such that none ofthe elements intersect one another. As such, in the illustratedembodiment, the adjacent sidewalls of individual elements are equallyspaced apart from one another. In such embodiments, the center-to-centerspacing of design elements (also referred to herein as pitch or simplyas p) may be greater than about 1.0 mm apart, such as from about 1.0 toabout 20 mm apart and more preferably from about 2.0 to about 10 mmapart. In one particularly preferred embodiment the continuous elementsare spaced apart from one-another from about 2.5 to about 4.0 mm apart.This spacing will result in a tissue web which generates maximum caliperwhen made of conventional cellulosic fibers. Further, this arrangementprovides a tissue web having three dimensional surface topography, yetrelatively uniform density.

In other embodiments the continuous elements may occur as wave-likepatterns that are arranged in-phase with one another such that the pitch(p) is approximately constant. In other embodiments elements may form awave pattern where adjacent elements are offset from one another.Regardless of the particular element pattern, or whether adjacentpatterns are in or out of phase with one another, the elements areseparated from one another by some minimal distance. Preferably thedistance between continuous elements is greater than 0.5 mm and in aparticularly preferred embodiment greater than about 1.0 mm and stillmore preferably greater than about 2.0 mm such as from about 2.0 toabout 6.0 mm and still more preferably from about 2.5 to about 4.0 mm.

Where the continuous elements are wave-like, the elements have anamplitude (A) and a wavelength (L). The amplitude may range from about2.0 to about 200 mm, in a particularly preferred embodiment from about10 to about 40 mm and still more preferably from about 18 to about 22mm. Similarly, the wavelength may range from about 20 to about 500 mm,in a particularly preferred embodiment from about 50 to about 200 mm andstill more preferably from about 80 to about 120 mm.

While in certain embodiments the structuring elements are continuous theinvention is not so limited. In other embodiments the elements may bediscrete. For clarity, the discrete elements will be referred to hereinas protuberances. Generally the protuberances are discrete and spacedapart from one another. Each protuberance is joined to a carrierstructure and extends outwardly from the web contracting plane ofthereof. In this manner the protuberances contact the tissue web duringmanufacture.

The protuberances may have a square horizontal and lateral (relative tothe plane of the carrier structure) cross-sectional shape, however, theshape is not so limited. The protuberance may have any number ofdifferent horizontal and lateral cross-sectional shapes. For example,the horizontal cross-section may have a rectangular, circular, oval,polygonal or hexagonal shape. A particularly preferred protuberance hasplanar sidewalls which are generally perpendicular to the plane of thecarrier structure. Alternatively, the protuberances may have a taperedlateral cross-section formed by sides that converge to yield aprotuberance having a base that is wider than the distal end.

The individual protuberances may be arranged in any number of differentmanners to create a decorative pattern. In one particular embodimentprotuberances are spaced and arranged in a non-random pattern so as tocreate a wave-like design. In the illustrated embodiment spaced betweenthe decorative patterns are landing areas that provide a visuallydistinctive interruption to the decorative pattern formed by theindividual spaced apart protuberances. In this manner, despite beingdiscrete elements, the protuberances are spaced apart so as to form avisually distinctive curvilinear decorative element that extendssubstantially in the machine direction. Taken as a whole the discreteelements form a wave-like pattern.

In other embodiments the protuberances may be spaced and arranged so asto form a decorative figure, icon or shape such as a flower, heart,puppy, logo, trademark, word(s), and the like. Generally the designelements are spaced about the support structure and can be equallyspaced or may be varied such that the density and the spacing distancemay be varied amongst the design elements. For example, the density ofthe design elements can be varied to provide a relatively large orrelatively small number of design elements on the web. In a particularlypreferred embodiment the design element density, measured as thepercentage of background surface covered by a design element, is fromabout 10 to about 35 percent and more preferably from about 20 to about30 percent. Similarly the spacing of the design elements can also bevaried, for example, the design elements can be arranged in spaced apartrows. In addition, the distance between spaced apart rows and/or betweenthe design elements within a single row can also be varied.

In certain embodiments the plurality of protuberances defining a givendesign element may be spaced apart from one another so as to definelanding areas there between. The landing areas are generally bounded bythe designs and coextensive with the top surface plane of the carrierstructure. Landing areas are generally permeable to liquids and allowwater to be removed from the cellulosic tissue web by the application ofdifferential fluid pressure, by evaporative mechanisms, or both whendrying air passes through the embryonic tissue web while on thepapermaking belt or a vacuum is applied through the belt.

The elements may be formed from a polymeric material, or other material,applied and joined to the carrier structure in any suitable manner. Thusin certain embodiments elements are formed by extruding, such as thatdisclosed in U.S. Pat. No. 5,939,008, the contents of which areincorporated herein by reference in a manner consistent with the presentinvention, or printing, such as that disclosed in U.S. Pat. No.5,204,055, the contents of which are incorporated herein by reference ina manner consistent with the present invention, a polymeric materialonto the carrier structure. In other embodiments the design element maybe produced, at least in some regions, by extruding or printing two ormore polymeric materials. In certain instances the polymeric materialmay be silicone or polyurethane, or a combination thereof.

The papermaking fabrics of the present invention are particularly usefulin making through-air dried tissue webs and products. Through-air dryingmanufacturing processes are well known in the art and may be eithercreped through-air drying (CTAD) or uncreped through-air drying (UCTAD)processes. In one embodiment the fabrics are useful in an UCTADmanufacturing process such as that described in U.S. Pat. No. 5,607,551.In that process a twin wire former having a papermaking headbox, such asa layered headbox, injects or deposits a stream of an aqueous suspensionof papermaking fibers onto a forming fabric positioned on a formingroll. The forming fabric serves to support and carry the newly-formedwet web downstream in the process as the web is partially dewatered to aconsistency of about 10 dry weight percent. Additional dewatering of thewet web can be carried out, such as by vacuum suction, while the wet webis supported by the forming fabric.

The wet web is then transferred from the forming fabric to a transferfabric. In one embodiment, the transfer fabric can be traveling at aslower speed than the forming fabric in order to impart increasedstretch into the web. This is commonly referred to as a “rush” transfer.Preferably the transfer fabric can have a void volume that is equal toor less than that of the forming fabric. The relative speed differencebetween the two fabrics can be from 0 to 60 percent, more specificallyfrom about 15 to 45 percent. Transfer is preferably carried out with theassistance of a vacuum shoe such that the forming fabric and thetransfer fabric simultaneously converge and diverge at the leading edgeof the vacuum slot.

The web is then transferred from the transfer fabric to the through-airdrying fabric with the aid of a vacuum transfer roll or a vacuumtransfer shoe, optionally again using a fixed gap transfer as previouslydescribed. The through-air drying fabric can be traveling at about thesame speed or a different speed relative to the transfer fabric. Ifdesired, the through-air drying fabric can be run at a slower speed tofurther enhance stretch. Transfer can be carried out with vacuumassistance to ensure deformation of the sheet to conform to thethrough-air drying fabric, thus yielding desired bulk and texture.

The side of the web contacting the through-air drying fabric istypically referred to as the “fabric side” of the paper web. The fabricside of the paper web, as described above, may have a shape thatconforms to the surface of the through-air drying fabric after the paperweb is dried in the throughdryer. The opposite side of the paper web, onthe other hand, is typically referred to as the “air side.”

The level of vacuum used for the web transfers can be from about 3 toabout 15 inches of mercury (75 to about 380 millimeters of mercury),preferably about 5 inches (125 millimeters) of mercury. The vacuum shoe(negative pressure) can be supplemented or replaced by the use ofpositive pressure from the opposite side of the web to blow the web ontothe next fabric in addition to or as a replacement for sucking it ontothe next fabric with vacuum. Also, a vacuum roll or rolls can be used toreplace the vacuum shoe(s).

While supported by the through-air drying fabric, the web is dried to aconsistency of about 94 percent or greater by the throughdryer andthereafter transferred to a carrier fabric. The dried basesheet istransported to the reel using the carrier fabric. Suitable carrierfabrics for this purpose are Albany International 84M or 94M and Asten959 or 937, all of which are relatively smooth fabrics having a finepattern. Optionally the base sheet may be subjected to additionalconverting steps such as reel calendering, off-line calendering orembossing.

TEST METHODS Fabric Image Analysis

Fabric images were acquired and analyzed using a Keyence VHX-5000Digital Microscope (Keyence Corporation, Osaka, Japan) equipped withVHX-5000 Communication Software Ver. 1.5.1.1. The lens is anultra-small, high performance zoom lens, VH-Z20R/Z20T.

Structuring element dimensions were measured using the Keyence software.For example, element height was measured by first drawing a lineapproximately along the top surface plane of the carrier structure withthe line tangent to at least two filaments forming the web contactingsurface of the carrier structure. A second parallel line has been drawnapproximately along the top surface plane of the structuring elementwith the line tangent to the top surface of the element. With the twolines drawn, each corresponding to a surface plane of the fabric, thedigital microscope software was instructed to calculate the distancesbetween the planes.

Element width was measured by determining the widest portion of theelement and using the software to draw a first line through the widestpoint, the line being substantially parallel to the web contactingsurface plane of the carrier structure. A pair of lines were then drawnperpendicular to the first line tangent to the point that the first lineintersected the element, the digital microscope software was instructedto calculate the distances between the pair of lines.

The surface area of the carrier structure covered by the structuringelements was measured using a Keyence Microscope and image analysissoftware described above. The sample of carrier structure formeasurement should be an undamaged, flat fabric swatch approximately 3×3inches in size.

An image of the fabric was acquired at a magnification of 20× and fromthe on-screen menu “Measure” was selected, followed by selection of“Auto” area measurement, then the “Color” option was selected and ameasurement was taken. Once a measurement was taken the structuringelements were filled using the “Fill” and “Eliminate Small Grains”features, followed by selecting a Shaping step. If there are areas ofthe structuring elements that needed to be filled in, or otherwiseedited to create an accurate 2-D highlight of the structuring elements,an accurate area representation was created by selecting “Edit”, “Fill.”The results were than tabulated by selecting the “Next” to proceed tothe Result Display step where “Measure Result” was selected and thecalculated Area Ratio Percent was displayed. FIG. 6 illustrates theoutput of the foregoing measurement method. The measurement was repeatedfor 3 distinct areas of the fabric sample and an arithmetic average AreaRatio Percent of the measurements was reported as the Area RatioPercent.

EXAMPLES

To evaluate the effect of structuring element size and coverage area onthe drying of tissue webs several different through-air drying fabricswere used to manufacture a single ply uncreped through-air dried(“UCTAD”) tissue web as generally described in U.S. Pat. No. 5,607,551,the contents of which are incorporated herein in a manner consistentwith the present invention. Tissue webs having a target bone dry basisweight of about 40 grams per square meter (gsm).

In all cases the base sheets were produced from a furnish comprisingnorthern softwood kraft and eucalyptus kraft using a layered headbox fedby three stock chests such that the webs having three layers (two outerlayers and a middle layer) were formed. The two outer layers comprisedeucalyptus (each layer comprising 30 percent weight by total weight ofthe web) and the middle layer comprised softwood and eucalyptus. Theamount of softwood and eucalyptus kraft in the middle layer wasmaintained for all inventive samples—the middle layer comprised 29percent (by total weight of the web) softwood and 11 percent (by totalweight of the web) eucalyptus. Strength was controlled via the additionof starch and/or by refining the softwood furnish.

The tissue web was formed on a Voith Fabrics TissueForm V formingfabric, vacuum dewatered to a consistency ranging from about 30 to about33 percent and then subjected to rush transfer when transferred to thetransfer fabric. The transfer fabric was the fabric described as “Fred”in U.S. Pat. No. 7,611,607 (commercially available from Voith Fabrics,Appleton, Wis.).

The web was then transferred to a through-air drying fabric comprising aprinted silicone pattern disposed on the sheet contacting side. Thesilicone formed a wave-like pattern on the sheet contacting side of thefabric. Inventive papermaking fabrics are shown in FIGS. 4 and 5. Thepattern properties of the various fabrics are summarized in Table 1,below.

TABLE 1 Element Element Element Element Coverage Height Width PerimeterAspect Area Fabric (mm) (mm) (mm) Ratio (%) 1 0.9 0.9 3.6 1:1 24 2 0.80.8 3.2 1:1 31 3 0.7 0.7 2.7 1:1 30 4 0.6 0.6 2.4 1:1 31 5 0.6 0.6 2.41:1 25

The tissue web was dried to a final consistency of about 98 percent bypassing the web over first and second through-air dryers while supportedby the through-air drying fabric. The exhaust temperature of the firstthrough-air dryer was controlled to about 300° F. It was discovered thatthrough-air drying fabrics having narrower structuring elements, whichare impermeable to air and water, were able to produce tissue webshaving a sufficient degree of smooth flat surfaces without negativelyaffecting drying. The plot shown in FIGS. 7 and 8 shows the heattransfer coefficient (shown in the equation below) calculated over thefirst through-air dryer for each fabric of the present example.

$h = \frac{{Drying}\mspace{14mu} {Rate}}{\left( {T_{supply} - T_{sheet}} \right)}$

In addition to varying the width of the elements the percent of coveragearea was varied by altering the spacing of the elements relative to oneanother. In each case the structuring elements had a substantiallysquare cross-sectional shape and an aspect ratio of 1:1. It was expectedthat the main factor affecting heat transfer coefficient would be therelative area of the fabric occluded by the elements and that for everyone percent increase in coverage there would be a one percent reductionin heat transfer. It was surprisingly discovered however, that thedimensions of the elements was a dominant factor affecting drying rate,and that using elements having a width of 0.7 mm or less the coveragearea could be increased with very little adverse effect on drying rate.

The drying benefit may also be determined by calculating the Drying LossFactor that compares the loss in drying rate measured for a given fabrichaving impermeable structuring elements (DR_(occluded)) to the dryingrate of a fabric devoid of such elements (DR_(open)):

${{Drying}\mspace{14mu} {Loss}\mspace{14mu} {Factor}} = \frac{1 - \frac{{DR}_{occluded}}{{DR}_{open}}}{{Coverage}\mspace{14mu} {Area}}$

Assuming that the area of the web in contact with the structuringelements are not drying at all, then the Drying Loss Factor will equal1, if it is drying just as well as the rest of the web then the DryingLoss Factor will be 0. FIG. 9 shows the Drying loss factor measured forthe fabrics of the present example compared to commercially availablethrough-air drying fabric that is void of structuring elements(designated as T-1205-2 and described previously in U.S. Pat. No.8,500,955). The Drying Loss Factor increases as the width of thestructuring element increases, however, for elements having a width of0.8 Drying Loss Factor increases more rapidly compared to elementshaving a width of 0.7 mm or less.

Accordingly, in a first embodiment the present invention provides apapermaking fabric comprising a woven carrier structure having a machineand a cross-machine direction and a first side with a plurality ofsubstantially machine direction oriented structuring elements disposedthereon, the structuring elements having a cross-sectional height andwidth, wherein the width is 0.7 mm or less and the aspect ratio is fromabout 2:1 to about 2:3

In a second embodiment the present invention provides the papermakingfabric of the first embodiment wherein the structuring elements arecontinuous line elements and have a polygonal cross-sectional shape.

In a third embodiment the present invention provides the papermakingfabric of the first or the second embodiments wherein the structuringelements have a cross-sectional shape selected from the group consistingof a trapezoid, a parallelogram, a rectangle, a rhombus, and a square.

In a fourth embodiment the present invention provides the papermakingfabric of the first through the third embodiments wherein thestructuring elements have a height from about 0.4 to 0.7 mm.

In a fifth embodiment the present invention provides the papermakingfabric of the first through the fourth embodiments wherein thestructuring elements have a perimeter from about 1.6 to about 2.4 mm.

In a sixth embodiment the present invention provides the papermakingfabric of the first through the fifth embodiments wherein thestructuring elements are impermeable to air and water and comprisesilicone or polyurethane.

In a seventh embodiment the present invention provides the papermakingfabric of the first through the sixth embodiments wherein thestructuring elements cover from about 28 to about 32 percent of thesurface area of the first side of the carrier structure.

We claim:
 1. A papermaking fabric comprising a woven carrier structurehaving a machine and a cross-machine direction and a first side with aplurality of continuous, substantially machine direction orientedstructuring elements disposed thereon, the structuring elements having across-sectional height and width, wherein the width is 0.7 mm or lessand the aspect ratio is from about 2:1 to about 2:3.
 2. The papermakingfabric of claim 1 wherein the structuring elements have a polygonalcross-sectional shape.
 3. The papermaking fabric of claim 2 wherein thestructuring elements have a cross-sectional shape selected from thegroup consisting of a trapezoid, a parallelogram, a rectangle, arhombus, and a square.
 4. The papermaking fabric of claim 1 wherein thestructuring elements have a height from about 0.4 to 0.7 mm.
 5. Thepapermaking fabric of claim 1 wherein the structuring elements have across-sectional perimeter from about 1.6 to about 2.4 mm.
 6. Thepapermaking fabric of claim 1 wherein the structuring elements areimpermeable to air and water and comprise silicone or polyurethane. 7.The papermaking fabric of claim 1 wherein the structuring elements coverfrom about 28 to about 32 percent of the surface area of the first sideof the carrier structure.
 8. The papermaking fabric of claim 1 whereinthe structuring elements have a rectangular cross section, a height fromabout 0.4 to 0.7 mm and a width from 0.4 to less than 0.7 mm and arespaced apart from one another at least about 1.0 mm.
 9. The papermakingfabric of claim 1 wherein the structuring elements have a substantiallysimilar cross-sectional shape, height and width and are disposedsubstantially parallel to one another and cover from about 28 to about35 percent of the first side of the carrier structure.
 10. A papermakingfabric comprising a woven carrier structure having a machine and across-machine direction and a first side with a plurality of continuous,substantially machine direction oriented air impermeable polymericstructuring elements disposed thereon, the structuring elements having atrapezoidal, square or rectangular cross-sectional shape, a height lessthan 0.7 mm and a width less than 0.7 mm.
 11. The papermaking fabric ofclaim 10 wherein the structuring elements have a height from about 0.4to 0.7 mm.
 12. The papermaking fabric of claim 10 wherein thestructuring elements have a cross-sectional perimeter from about 1.6 toabout 2.4 mm.
 13. The papermaking fabric of claim 10 wherein thestructuring elements cover from about 28 to about 35 percent of thesurface area of the first side of the carrier structure.
 14. Thepapermaking fabric of claim 10 wherein the structuring elements have asubstantially similar cross-sectional shape, height and width and aredisposed substantially parallel to one another and cover from about 28to about 35 percent of the first side of the carrier structure.
 15. Apapermaking fabric comprising a woven carrier structure having a machineand a cross-machine direction and a first side with a plurality ofcontinuous, substantially machine direction oriented air impermeablepolymeric structuring elements disposed thereon and covering from about28 to about 35 percent of the first side of the carrier structure,wherein the plurality of structuring elements are substantiallysimilarly shaped, each having a polygonal cross-sectional shape, anaspect ratio from about 1.5:1 to about 1:1 and a width less than 0.7 mm.16. The papermaking fabric of claim 15 wherein the structuring elementshave a height from about 0.4 to about 0.7 mm.
 17. The papermaking fabricof claim 15 wherein the structuring elements have a cross-sectionalperimeter from about 1.6 to about 2.4 mm.
 18. The papermaking fabric ofclaim 15 wherein the structuring elements cover from about 28 to about32 percent of the surface area of the first side of the carrierstructure.
 19. The papermaking fabric of claim 15 wherein thestructuring elements have a substantially planar top surface and theelements have substantially similar heights ranging from about 0.4 toabout 0.7 mm.
 20. The papermaking fabric of claim 15 wherein thestructuring elements have a width from about 0.4 to less than 0.7 mm.